Such valves are known in diverse ways from the prior art. In the capacity of a proportional valve, it must be suitable for making available, at the working port provided for connection of the pneumatic fitting, a (an air) pressure that can be regulated as precisely as possible. For this purpose, various valve positions are typically approached by appropriate actuation of the valve by means of the actuating element, in order optionally to couple the working port fluidically with the compressed-air supply or with the vent or (in order to maintain a pressure prevailing at a working port) to decouple it from both. In this connection, intermediate positions between complete air admission and complete venting of the fitting connected to the working port should also be possible in the capacity of a proportional valve.
For clarification, it must be mentioned that any actuators capable of being actuated pneumatically, and therefore especially also a pneumatic drive, are to be understood as a pneumatic fitting in the present context.
Proportional valves of the type mentioned in the foregoing are relatively complex in their design and their operation.
In this connection, the prior art frequently utilizes so-called slide valves, in which at least one linearly displaceable valve element, depending on its position, either opens or closes (completely or partly) an opening disposed laterally relative to the valve element and influencing the flow of air. In contrast to poppet valves, however, for lack of a sealing seat that effectively blocks the flow of fluid, detrimental leakage, which the present disclosure aims advantageously to keep as small as possible or to prevent entirely, must always be expected here for precise application situations.
Beyond this, a proportional valve of the class in question is already known from DE 10 2012 017 713 A1. It has the form of a position controller, in which a power stage (actuated by a preliminary stage functioning as an actuating element) comprises, as a pressure-displacement transducer, two spring-preloaded poppet valves, which are pressurized from a common control chamber and which are sequentially actuated in order to realize various switched states upon increase of the pressure prevailing in the control chamber. Because of the poppet valves to be disposed therein on various sides of the common control chamber, the position controller described in DE 10 2012 017 713 A1 needs a not inconsiderable installation space, which the present disclosure intends to further reduce.
From U.S. Pat. No. 2,850,330, a valve group provided for use in a brake system for tractors with trailers is known in which, by realization of two valves, three valve elements in total are provided that are connected in series, are respectively movable in an axial direction and are positionable in cascade-like manner. By means of the first valve, it is now optionally possible to vent a first working port for the brake system of the trailer or optionally to place it in communication with a compressed-air port on the tractor side, while by means of the second valve it is optionally possible to vent a second emergency working port for the brake system of the trailer or to place it in communication with a second emergency compressed-air port on the tractor side. During variation of the position of the first valve element, a transition takes place there from a first switched state, in which the respective working port is vented, respectively to a second switched state, in which the respective working port is in communication with the compressed-air port on the tractor side.